1) Field
Embodiments of the present invention pertain to the field of semiconductor processing and, in particular, to methods of three-dimensional (3D) structure fill.
2) Description of Related Art
Semiconductor wafer processing may involve forming and filling trenches in semiconductor wafers or substrates. Filling trenches in a semiconductor wafer or substrate with a material may be referred to as “gap fill.” Gap fill is used in a variety of applications, such as in the formation of through-silicon vias (TSVs). As trench widths become narrower and trench aspect ratios increase, the process of filling trenches becomes more challenging.
One existing gap fill method is spin-coating. Spin-coating typically involves coating a wafer or substrate with a liquid material with a spin-coating machine. Spin-coating machines may include a spin track that holds and rotates the wafer or substrate, and a nozzle at the center of the spin track that dispenses the liquid material. The spin-coating machine rotates the wafer or substrate, and thus distributes the material throughout the wafer surface and into the trenches. In spin-coating methods, a solvent is used to control the viscosity of the liquid material dispensed, which introduces impurities into the filled trenches. Impurities in the filled trenches can reduce performance and yield of devices formed with the filled trenches. Furthermore, spin-coating involves post-processing steps after depositing the liquid material, such as curing the deposited material.
Another existing gap fill method involves deposition of the fill material via chemical vapor deposition (CVD), atomic layer deposition (ALD), plasma-enhanced chemical vapor deposition (PECVD), or physical vapor deposition (PVD). CVD, ALD, PECVD, and PVD methods of filling trenches typically result in deposition of more material on the upper sidewalls of the trenches than on the bottom and lower sidewalls of the trenches. Such methods also result in more deposited material on the top surfaces adjacent to the trenches. FIG. 1 illustrates a cross-sectional view of a semiconductor wafer 100 with trenches 101 that have been filled via such a deposition process. The deposition process deposits more of the material 103 on the upper portions of the trench sidewalls 104 and top surfaces 108 than at the bottoms 102 of the trenches 101. The uneven deposition forms overhangs, which can cause the trench openings to close prior to completely filling the gap, resulting in voids 106.
Gap fill defects such as unwanted voids can result in poor device performance, defective devices, and high variability die-to-die or wafer-to-wafer.